The present invention relates to a light transmission system for transmitting a light beam of a variable wave-length from a light source to a light receiver, an apparatus for measuring a change in distance between an optical element and an object member movable with respect to each other by using the light transmission system, and an apparatus for exposing at least a part of a surface of the object member (for example, a recording medium) by using the light transmission system.
TECHNICAL DIJEST of INTERNATIONAL SYMPOSIUM ON OPTICAL MEMORY 1998 discloses on Pd-07 regarding Deep UV mastering using an all-solid-state 266 nm laser for an over 20 GB/layer capacity disk that a positional relationship between an objective lens and a recording disk is measured from a position on a light receiver at which position a first light beam projected through the objective lens to the recording disk and subsequently reflected by the recording disk is received by the light receiver, while a second light beam is projected through the objective lens to the recording disk to expose a surface of the recording disk.
An object of the present invention is to provide a light transmission device for transmitting securely and efficiently a light beam with a variation of wavelength from a light source to a light receiver while restraining a position on the light receiver at which position the light beam impinges from changing according to the variation of wavelength of the light beam, an apparatus for measuring correctly irrespective of the variation of wavelength of the light beam a change in distance between an optical element and a surface of an object member movable relative to each other, and an apparatus for exposing securely irrespective of the variation of wavelength of the light beam at least apart of a surface oaf object member (for example, a recording medium).
A light transmission device for transmitting a light beam with a variation of wavelength from a light source to a light receiver, according to the present invention, comprises, an optical element for receiving the light beam and projecting the light beam wherein a deflection angle between the received light beam and the projected light beam varies according to the variation of wavelength of the light beam, and a compensation optical element for receiving the light beam and projecting the light beam wherein a compensating deflection angle between the received light beam and the projected light beam varies according to the variation of wavelength of the light beam, wherein the optical element and the compensation optical element are arranged optically in series between the light source and the light receiver (the light beam may proceed from the optical element to an object, and subsequently the light beam reflected by the object may return to the optical element to proceed further toward the light receiver), the deflection angle changes in a first direction according to an increase (decrease) of wavelength of the light beam, the compensating deflection angle changes in a second direction according to the increase (decrease) of wavelength of the light beam, and the change of the deflection angle in the first direction is compensated by the change of the compensating deflection angle in the second direction so that a position on the light receiver at which position the light beam impinges is restrained from changing according to the increase (decrease) of wavelength of the light beam.
Since the change of the deflection angle in the first direction at the optical element is compensated by the change of the compensating deflection angle in the second direction at the compensation optical element so that the position on the light receiver at which position the light beam impinges is restrained from changing according to the increase (decrease) of wavelength of the light beam, the light beam is transmitted securely and efficiently from the light source to the light receiver although the deflection angle of the optical element is changed according to the variation of wavelength of the light beam.
The optical element and the compensation optical element may be arranged in such a manner that the light beam r received by the optical element, the light beam projected by the optical element, the light beam received by the compensation optical element and the light beam projected by the compensation optical element proceed along an imaginary plane. The optical element may be a lens. The compensation optical element may be a prism, diffraction grating or lens.
It is effective for compensating the change of the deflection angle in the first direction at the optical element by the change of the compensating deflection angle in the second direction that the optical element and the compensation optical element are arranged in such a manner that on an imaginary plane to be traversed by the light beam with a predetermined angle between the imaginary plane and the light beam, a direction in which a position on the imaginary plane to be passed by the light beam is changed by the change of the deflection angle according to the increase (decrease) of wavelength of the light beam is opposite to a direction in which the position on the imaginary plane to be passed by the light beam is changed by the change of the compensating deflection angle according to the increase (decrease) of wavelength of the light beam.
It is preferable that the compensation optical element is arranged to receive the light beam projected by the optical element and to project the light beam toward the light receiver, that is, the compensation optical element is arranged at a downstream side of the optical element in a light beam proceeding direction.
It is effective for compensating the change of the deflection angle in the first direction at the optical element by the change of the compensating deflection angle in the second direction that a direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the deflection angle in the first direction is opposite to a direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the compensating deflection angle in the second direction.
It is effective for compensating the change of the deflection angle in the first direction at the optical element by the change of the compensating deflection angle in the second direction that the optical element and the compensation optical element are arranged in such a manner that the light beam received by the optical element, the light beam projected by the optical element, the light beam received by the compensation optical element and the light beam projected by the compensation optical element proceed along or on an imaginary plane, and the first direction is opposite to the second direction as seen in a proceeding direction of the light beam.
The optical element may be adapted to face to an object member, and the light beam projected by the optical element may be received by the light receiver after being reflected by the object member. When the optical element is a lens, the lens is arranged to prevent the light beam from proceeding along a symmetrical axis of the lens around which symmetrical axis the lens is substantially symmetrical, so that the deflection angle of the light beam at the optical element changes according to the change of wavelength of the light beam. The light transmission device may further comprise a supplemental lens arranged to convert the light beam projected by the light source to a convergent light to be received by the optical element. When the optical element and the object member are movable relative to each other, the optical element is arranged to prevent a direction in which the light beam proceeds from the optical element to the object member from being parallel to a direction in which the optical element and the object member are movable relative to each other, so that the position on the light receiver at which position the light beam impinges is changed in accordance with the mutual movement between the optical element and the object member or a change in distance therebetween.
The optical element may be movable to change the position on the light receiver at which position the light beam impinges in accordance with the movement of the optical element. At least one of refractive angle and diffractive angle of the light beam at the optical element and at least one of refractive angle and diffractive angle of the light beam at the compensation optical element may vary according to the variation of wavelength of the light beam. The lens of the compensation optical element may include a pair of a convex lens and a concave lens, the convex lens and the concave lens may be arranged in such a manner that the light beam projected by the concave lens is received by the convex lens, a curvature of a surface of the concave lens facing to the convex lens and a curvature of a surface of the convex lens facing to the concave lens are larger than a curvature of a surface of the convex lens from which the light beam is projected.
An apparatus for measuring a change in distance between an optical element and a surface of an object member movable relative to each other, according to the invention, comprises, a light source for generating a light beam with a variation of wavelength, a light receiver for receiving the light beam reflected by the surface to measure a change of a position on the light receiver at which position the light beam impinges corresponding to the change in distance between the optical element and the surface of the object member, and a compensation optical element for receiving the light beam and projecting the light beam wherein a compensating deflection angle between the received light beam and the projected light beam varies according to the variation of wavelength of the light beam,
wherein the optical element is arranged to receive the light beam and project the light beam toward the surface of the object member, a deflection angle of the optical element between the received light beam and the projected light beam varies according to the variation of wavelength of the light beam, the optical element and the compensation optical element are arranged optically in series between the light source and the light receiver, the deflection angle changes in a first direction according to an increase of wavelength of the light beam, the compensating deflection angle changes in a second direction according to the increase of wavelength of the light beam, and the change of the deflection angle in the first direction is compensated by the change of the compensating deflection angle in the second direction so that the position on the light receiver at which position the light beam impinges is restrained from changing according to the increase of wavelength of the light beam.
Since the change of the deflection angle in the first direction at the optical element is compensated by the change of the compensating deflection angle in the second direction at the compensation optical element so that the position on the light receiver at which position the light beam impinges is restrained from changing according to the increase (decrease) of wavelength of the light beam, the change of the position on the light receiver at which position the light beam impinges corresponds correctly to the change in distance between the optical element and the surface of the object member although the deflection angle of the optical element is changed according to the variation of wavelength of the light beam, so that the distance between the optical element and the surface of the object member is correctly measured.
The optical element is arranged to prevent a direction in which the light beam proceeds from the optical element to the surface of the object member from being parallel to a direction in which the optical element and the surface of the object member are movable relative to each other, so that the position on the light receiver at which position the light beam impinges is changed in accordance with the mutual movement between the optical element and the object member or a change in distance therebetween. The change of the position on the light receiver at which position the light beam impinges may be a difference between a desired position on the light receiver (for example, a datum or reference position of the light receiver) and a position on the light receiver at which position the first light beam actually impinges.
A direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the deflection angle in the first direction is opposite to a direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the compensating deflection angle in the second direction, and/or the optical element and the compensation optical element are arranged in such a manner that on an imaginary plane to be traversed by the light beam with a predetermined angle between the imaginary plane and the light beam, a direction in which a position on the imaginary plane to be passed by the light beam is changed by the change of the deflection angle according to the increase (decrease) of wavelength of the light beam is opposite to a direction in which the position on the imaginary plane to be passed by the light beam is changed by the change of the compensating deflection angle according to the increase (decrease) of wavelength of the light beam, so that the change of the deflection angle in the first direction is compensated by the change of the compensating deflection angle in the second direction.
An apparatus for exposing at least a part of a surface of a object member, according to the present invention, comprises, a first light source for generating a first light beam with a variation of wavelength, a second light source for generating a second light beam, an optical element for receiving the first and second light beams and projecting the first and second light beams toward the surface of the object member, wherein the surface of the object member and the optical element are movable relative to each other, a deflection angle between the received first light beam and the projected first light beam varies according to the variation of wavelength of the first light beam, and the second light beam is focused on the at least a part of the surface of the object member by the optical element to expose the at least a part of the surface of the object member, a light receiver for receiving the first light beam reflected by the surface to measure a change of a position on the light receiver at which position the first light beam impinges corresponding to a change in distance between the optical element and the surface of the object member, a compensation optical element for receiving the first light beam and projecting the first light beam wherein a compensating deflection angle between the received first light beam and the projected first light beam varies according to the variation of wavelength of the first light beam, and an optical element positioner for moving the optical element relative to the surface of the object member on the basis of the measured change of the position on the light receiver at which position the first light beam impinges,
wherein the optical element and the compensation optical element are arranged optically in series between the light source and the light receiver, the deflection angle changes in a first direction according to an increase of wavelength of the first light beam, the compensating deflection angle changes in a second direction according to the increase of wavelength of the first light beam, and the change of the deflection angle in the first direction is compensated by the change of the compensating deflection angle in the second direction so that the position on the light receiver at which position the first light beam impinges is restrained from changing according to the increase of wavelength of the first light beam.
Since the change of the deflection angle in the first direction at the optical element is compensated by the change of the compensating deflection angle in the second direction at the compensation optical element so that the position on the light receiver at which position the light beam impinges is restrained from changing according to the increase (decrease) of wavelength of the light beam, the change of the position on the light receiver at which position the light beam impinges corresponds correctly to the change in distance between the optical element and the surface of the object member although the deflection angle of the optical element is changed according to the variation of wavelength of the light beam, so that the distance between the optical element and the surface of the object member is correctly measured. Therefore, the optical element is moved on the basis of the correctly measured change of the distance between the optical element and the surface of the object member, the optical element is moved on the basis of the correctly measured change of the distance between the optical element and the surface of the object member to keep the distance between the optical element and the surface of the object member at a desirable value and/or to change the distance between the optical element and the surface of the object member to the desirable value, so that the second light beam is correctly focused on the surface of the object member to expose securely the at least a part of the surface of the object member.
The optical element is arranged to prevent a direction in which the light beam proceeds from the optical element to the surface of the object member from being parallel to a direction in which the optical element and the surface of the object member are movable relative to each other, so that the position on the light receiver at which position the light beam impinges is changed in accordance with the mutual movement between the optical element and the object member or a change in distance therebetween.
A direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the deflection angle in the first direction is opposite to a direction in which the position on the light receiver at which position the light beam impinges is changed according to the change of the compensating deflection angle in the second direction, and/or the optical element and the compensation optical element are arranged in such a manner that on an imaginary plane to be traversed by the light beam with a predetermined angle between the imaginary plane and the light beam, a direction in which a position on the imaginary plane to be passed by the light beam is changed by the change of the deflection angle according to the increase (decrease) of wavelength of the light beam is opposite to a direction in which the position on the imaginary plane to be passed by the light beam is changed by the change of the compensating deflection angle according to the increase (decrease) of wavelength of the light beam, so that the change of the deflection angle in the first direction is compensated by the change of the compensating deflection angle in the second direction.
The measured change of the position on the light receiver at which position the first light beam impinges may be a difference between a desired position on the light receiver and a position on the light receiver at which position the first light beam actually impinges, and the optical element positioner moves the optical element relative to the surface of the object member to decrease the difference. The desired position on the light receiver may correspond to a desired distance between the optical element and the surface of the object member.
It is effective for decreasing a positioning error value for focusing the second light beam on the surface of the object member that the variation of the deflection angle between the first light beam received by the optical element and the first light beam projected by the optical element is larger than a variation of a deflection angle between the second light beam received by the optical element and the second light beam projected by the optical element, and/or the variation of wavelength of the first light beam is larger than a variation of wavelength of the second light beam. When a wavelength of the second light beam is not more than 300 nm, the compensation of the first light beam by the compensation optical member is important.